Tailing problem during PAH's analysis. GC/MS 7820A/5977E

Hello everyone,

Our system is 7820A/5977E we have a tailing problem during PAH's analysis.

The method we used is:

Injection Volume: 1 µl

55 C held for 5 min, 25 C/min to 320 C, held for 3 min

Carrier gas: He 1.5 ml/min

Column: HP 5: 30m x 0,25 mm x 0,25 µm

Liner: 4mm id, dual taper deactivated, no wool

Mode: P.Splitless

Acquisition mode: EI, SIM (1 to 200 pg)

Aux: 290 C, Ions Source:340 C, MS Quad: 150 C

What we made until now is:

Cleaning the Inlet and the ion source, using different Liners. increase Transfer line temperature to 340 C. Change the column, new pre, and post-column, Septa and O-Ring, different solvents, bake out the MSD, and different PAHs standards.

 

Air/Water check:

18/69 = 0.59 Water% (counts=5538)

28/69 = 2.36 Nitrogen% (counts=22200)

32/69 = 1.29 Oxygen% (counts=12140)

44/69 = 0.17 Carbon Dioxide% (counts=1586)

 

 

Any comments and suggestions will be appreciated

Parents
  • Hello

    There are several things that can cause tailing, Is this tailing in all peaks, or just the first ones?

    At our GC Troubleshooting Guide a few solutions are suggested (you already made some of them):

    https://www.agilent.com/cs/library/posters/public/5994-0451EN_GC_Troubleshooting_Guide%20poster_LR.pdf

    What else I suggest to check:

    - your initial temperature ramp is in according to the vial solvent? Try to decrease a little this T

    - Cut ~10 cm at the beginning of the column;

    - a more inert column can be used to help (HP-5ms UI or DB-5ms UI)

    Thank you,

     

  • Hello Marianabaptistao,

    thank you for your comment.

    - Cut ~10 cm at the beginning of the column;

    I trimmed the beginning of the column but forgot to write it above.

    your initial temperature ramp is in according to the vial solvent? Try to decrease a little this T

    I used many solvents and always used an initial temperature of 5 C below the solvent's boiling point. But it still tailing.

    Attached is a 50 ppb chromatogram for EPA PAH standard 50 ppb

  • Hello

    Did you have any other moment that you could see no tailing using this method and this column or this is a new method beinf developed?

    I can see that all compounds are tailing, even the last ones. A few more things you can try:

    - Try to reinstall the column;

    - Did you check inlet contamination? the column is solvent rinsable if needed;

    Lastly but important, some compounds can tail by their own and it's not about the column or the system - just that they are more reactive. In this situation, the best is to use more inert columns. Please see an app note with DB-5ms UI column for PAH standards, no problem at all and still 10 times lower than 50 ppb: https://www.agilent.com/cs/library/applications/5990-5652EN.pdf

    If is not working at all, try the MS Ultra Inert version of this column.

    Thank you

  • Hello  

    Did you have any other moment that you could see no tailing using this method and this column or this is a new method beinf developed?

    No,  the tailing has been seen since the PAHs method was developed.

    To test the Instrument's performance, I bought an Alkan Standard C10-C40. The peaks also show slight tailing (Symmetry between1.1 and 1.6)
    I cleaned also the injector and reinstalled the column.

    Do you think it's a PAHs issue or an instrument issue? In the literature, this column has been widely used for PAHs without any problems.

    Thank you for your helpful suggestions.

  • Hello ,

    It could be both, but if you are seeing tailing problemas also with standars it suggests to be more likely an instrument issue. Since you already trimmed the column and re installed it, looks like everything is checked. How did you clean the injector? This clean helped at all?

    Do you run any other methods in this GC to compare, in addition to alkan standards?

    If everything was checked and its OK, I still continue to suggest to evaluate an UI column. I know many cases the HP-5 could work but it depends on PAH concentration, types of PAHs, your matrix and other individual parameters from each application to determine if the inertness is enough or not. Maybe this is one of the situations where each detail in the instrument and in the column will help you to get more symetric peaks.

    Thank you

  • Hello ,

    I'm sorry, but I was sick, so I couldn't reply to you. I cleaned the injector according to Agilent instructions and it didn't help. I ordered also the DB-5ms UI column, I will install it maybe next week and let you know if it is better or not.

    We are aiming to measure PAHs and their derivates in the sampled ambient air filter. The estimated concentration is at the ppb level.

    Thank you

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